1. Field
The following description relates to heterocyclic compounds and organic light emitting devices comprising the same.
2. Description of the Related Art
Organic light-emitting diodes (OLEDs), which are self-emitting diodes, have advantages such as wide viewing angles, excellent contrast, quick response, high brightness, excellent driving voltage characteristics, or can provide multicolored images.
A typical OLED has a structure including a substrate, and an anode, a hole transport layer, an emission layer, an electron transport layer, and a cathode which are sequentially stacked on the substrate. The hole transport layer, the emission layer, and the electron transport layer are organic thin films formed of organic compounds.
An operating principle of an OLED having the above-described structure is as follows.
When a voltage is applied between the anode and the cathode, holes injected from the anode move to the emission layer via the hole transport layer, and electrons injected from the cathode move to the emission layer via the electron transport layer. The holes and electrons recombine in the emission layer to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted.
The most important factor determining the emission efficiency in the OLED is the emission materials. Fluorescent materials have been used as the emission materials until now; however, a development of phosphorescent materials is theoretically one of the best ways to improve the emission efficiency up to four times. Until now, iridium (III) complex-based materials have been used as phosphorescent emission materials, and with respect to each red, green and blue color (RGB), (acac)Ir(btp)2, Ir(ppy)2, Firpic, or the like are used.

In regards to materials for a phosphorescent illuminant, CBP is the most widely used until now. Also, high efficiency OLEDs including hole blocking layers such as BCP and BAlq are used, and high performance OLEDs using BAlq derivatives as hosts are used by Pioneer Co., or the like in Japan.

Although existing materials have good emission characteristics, the existing materials have a low glass transition temperature and a very poor thermal stability, causing problems such as changes in materials when the existing materials are subject to a high temperature deposition process under a vacuum condition. Since electric power efficiency of OLED=(π/voltage)×current efficiency, the electric power efficiency is inversely proportional to the voltage, and accordingly, the electric power efficiency must be great in order for an electric power consumption of the OLED to be low. An OLED using the phosphorescent materials actually has a substantially greater current efficiency (cd/A) compared to that of an OLED using fluorescent materials, but when materials, such as BAlq, CBP, or the like is used as the host for the phosphorescent materials, a driving voltage of the OLED using the phosphorescent materials is greater than that of the OLED using the fluorescent materials, and thus, there is no substantial enhancement in regards to the electric power efficiency (lm/w). Also, a lifespan of the OLED using the phosphorescent materials is not satisfactory. Thus, a host material having a better performance is required.